1. Field of the Invention
The present invention relates to a facsimile apparatus, and in particular to a facsimile apparatus with error correcting function.
2. Related Background Art
Conventional facsimile apparatus with error correction mode (or error resending mode) is provided with a memory space (or memory area) for error image resending, in addition to a memory space for substituted reception.
In the conventional error resending mode, upon detection of an error, the receiver unit sends a NACK (non-acknowledgement) signal through a backward channel thereby interrupting the transmission from the transmitter unit. In this case, a large memory is not required in the receiver unit since it can consecutively decode and record error-free data. Also the transmitter unit can identify proper data reception by the receiver unit if the NACK signal is not received within a predetermined time after the transmission of data of a frame, and can store new data in a memory space used for storing the transmitted data. Said predetermined time is variable depending for example on the frame size, ability for detecting the NACK signal, and tolerance for the delay in the transmission channel, but can be, for example, about 5 seconds. For a data transmission rate of 9600 h/s, the memory space required for the data during 5 seconds is 6 Kbytes, so that a large memory capacity is not required.
However, the error correction mode at least requires a memory capacity of 64 Kbytes, or 128 Kbytes if a double buffer structure (each buffer with 64 Kbytes) is adopted for reducing the flow control (control for interruption). A memory capacity of 128 Kbytes can store 6 to 7 sheets of CCITT No. 1 chart when transmitted in the standard mode.
Thus, the use of a separate memory space for the above-explained memory correction, in addition to the memory space for memory communication mode, is quite inefficient in consideration of the effective utilization of the momory spaces.
In relation to the error resending mode, the present applicant already filed U.S. patent applications Ser. Nos. 110,542 (Oct. 20, 1987), now U.S. Pat. No. 4,829,524, 847,684 (Apr. 3, 1986,), now U.S. Pat. No. 4,885,755 and 162,266 (Feb. 26, 1988), now U.S. Pat. No. 4,897,831.